Stacks of printed products, such as newspapers, magazines or brochures are produced in particular for dispatch. Such stacks are made into packages by strapping and/or wrapping. If produced for retailer supply, such packages frequently contain varying numbers of printed products of different product types. For producing the packages, the products of the different product types are e.g. taken from storage formations (rolls, bundles, stacks, packages) or they are supplied to the stacking operation on-line, i.e. directly from the printing press.
According to the prior art, stacks or packages of printed products are produced, for example, by conveying an imbricated stream of the printed products to be stacked to a stacking shaft and by depositing the products in the stacking shaft. When the stack being produced in the stacking shaft has reached a predefined height or when it contains a predefined number of printed products, it is pushed out of the stacking shaft, if so required directly into a strapping device, in which the stack is strapped or wrapped.
For producing stacks containing products of different types, a device carrying the stack being produced is moved to a plurality of feed points, wherein at each feed point products of one product type are added. Alternately, a supply stream is to be established, in which the products of different types are supplied to the stacking operation in the sequence required by the sequence of packages to be produced.
Establishing supply streams of printed products of different product types is known, for example, from the book-binding industry, where, streams of signatures are supplied to, for example, stitching or stapling or binding machines. In such streams, the different signatures are arranged in the sequence of the books to be produced. Establishment of such streams is described, for example in the publication EP-579940 (Kolbus GmbH). One signature type is deposited on a conveyer belt from each one of a row of feed points arranged above the conveyor belt. Therein the sequence in which the signature types are assigned to the feed points is the same as the sequence of the signatures in the book block and the feed points and the conveyor belt are synchronised in such a manner, that signatures are deposited on the conveyor belt as imbricated stream sections, each of which corresponds to a book block. This means, that each stream section contains one signature of each type, the signatures being arranged in the correct sequence for the book to be produced.
Because for every book one signature of each type is to be deposited, the system according to EP-0579940 can be operated in a regularly clocked manner, the speed of the conveyor belt being adjusted in such a manner, that in each conveying clock cycle it advances by a distance corresponding to the distance between two feed points plus the required scale spacing. Signature supply at the feed points is adapted to the ratio of the length of the imbricated stream formations to be established and the distances between the feed points. If the distance between the feed points is greater than the length of the imbricated stream sections to be established, a signature is supplied at each feed point in each clock cycle. If the distance between the feed points is smaller than the length of the imbricated stream sections to be established, for example, imbricated stream sections are associated to only e.g. every second or third clock cycle and supply at the feed points is controlled correspondingly.
The system as shortly described above can also be used for establishing imbricated stream sections each containing only selected types of the flat articles available from the feed points. Such individualized stream sections can e.g. constitue groups of supplements to be added to daily newspapers which are such adapted to individual customer needs. For such individualisation of the imbricated stream sections, supply of selected ones of the supplements is suppressed in corresponding clock cycles. The system itself, however, can still be operated rigidly clocked. However, the system does not allow deposition of more than one article from the same feed point in the same imbricated stream section and it does not allow changes in the sequence of the articles in the imbricated stream sections.
A system for establishing a stream of different printed product types, which system does not have the limitations mentioned above, is described in the publication EP-1029705. This system comprises a continuously operated gripper conveyor, with the help of which the products in the stream to be established are conveyed individually held by individual grippers at a regular distance between one another and with an essentially constant speed. For every feed point a conveying system is provided, which comprises individually movable grippers. These are loaded with one product each and are buffered behind the feed point. In correspondence with the product sequence to be established, buffered products are released from the buffers and transferred to corresponding grippers of the gripper conveyor. The stream established in this system is not subject to any conditions with respect to the number and the sequence of products of different types within the stream. This very high flexibility, however, is paid for by a very elaborate device and a relatively elaborate control system. Operation of the system is again rigidly clock cycled. In every cycle a gripper of the gripper conveyor is positioned at every feed point making transfer of one product possible. Transfers are selectively activated or suppressed in correspondence with the product sequence to be established.